This invention relates to a mechanical device having an axially aligned, linear axial movement between its components, and, more particularly, to a preloading arrangement that prevents backlash in the movement.
A number of types of mechanical devices include components that translate relative to each other while maintaining a precisely defined, axially aligned relationship. In an example of interest to the inventor, an optical zoom lens requires that tubular housings containing the optical elements translate along an optical axis to change the spacings of the optical elements. The housings may rotate about the optical axis, but must remain well-aligned along the optical axis so that the optical signal is not distorted.
For some zoom lenses, backlash and play in the movement is not a concern. However, in sophisticated zoom lens systems such as found in some sensing devices and display devices, there can be no backlash or play between the housings, as for example when the direction of axial movement is changed. The presence of backlash may lead to errors in the determination of the exact power of magnification of the zoom lens and in turn lead to errors in the output of the system.
Mechanical structures are available to prevent backlash in such mechanical systems having a linear axial movement. Precisely machined multi-start helicoil threads are sometimes used. In another approach, accurately positioned slot-and-pin arrangements have been employed, but these structures require post-fitting operations and extreme accuracy. These approaches are operable, but are expensive to implement because they require a high degree of precision. Additionally, the closely fitted elements may be susceptible to change when the temperature of operation changes. The latter is particularly of concern where different ones of the components are made of different materials so that the fit between them changes as a result of temperature changes.
There is a need for a simpler, less-complex, and less-expensive approach to the prevention of backlash and play in mechanical systems having a linear axial movement. The present invention fulfills this need, and further provides related advantages.